1. Field of the Invention
The present invention relates to a fluorescent endoscope system and a method for imaging diagnostic objects using the same, and more particularly to a fluorescent endoscope system having an improved image detection module for accurate and efficient diagnosis of tumors in the human body and a method for imaging in vivo diagnostic objects using the same.
2. Description of the Prior Art
As generally known in the art, a vesical fluorescent endoscope has been developed by Karl Storz GmgH, Germany, and used for vesical tumor diagnosis. It uses an optical source of white light and provides detailed observation of the surface of an internal organ as a normal endoscope system. Furthermore, it also uses an optical source (e.g., D-LIGHT) of blue light as excitation light, which is composed of a xenon lamp and an optical fiber, and provides fluorescent observation of dubious parts induced by a contrast medium (e.g., ALA).
The above fluorescent endoscope provides visual inspection and fluorescent observation of dubious parts with Endovision Telecom SL-PDD, which is a TV camera having a single high-sensitivity color chip. In a fluorescent diagnostic mode, an optical filter is positioned in front of the TV camera to interrupt excitation light reflected from a diagnostic object. The optical filter is designed in such a manner that a part of the reflected excitation light reaches the camera detector because, if the reflected excitation light is completely interrupted, the observer (e.g., a physician) cannot correctly recognize from where fluorescent light is generated. Such partial transmission of excitation light through the optical filter helps the physician to grasp the position and direction of the diagnostic object by observing the background portion which does not emit fluorescent light on the screen in the fluorescent diagnostic mode.
However, the above-mentioned conventional fluorescent endoscope system has problems as follows: the color TV camera of the fluorescent endoscope system, which basically has lower sensitivity than monochrome cameras, cannot accurately perceive faint fluorescent light emitted from the diagnostic object and, in particular, cannot be used when an endoscope having a small aperture ratio is necessary. Furthermore, optical noise increases and faint fluorescent light cannot be perceived, because reflected excitation light is partially transmitted. The color TV camera used in the above fluorescent endoscope system also has non-linear characteristics regarding optical signals. In summary, poor sensitivity to fluorescent light and existence of optical noise make diagnosis through quantitative fluorescent observation impossible.
In order to solve these problems, a fluorescent endoscope system having two channels has been proposed in Korean Registered Patent No. 0411631 of Uk Kang and G. V. Papayan, entitled “FLUORESCENT ENDOSCOPE SYSTEM AND METHOD FOR IMAGING DIAGNOSTIC OBJECTS USING THE SAME.” The proposed system includes an endoscope assembly having an optical cable and an optical source module connected to the assembly. The light module irradiates white light for use in a normal endoscope mode and/or excitation light of short wavelength for use in a fluorescent inspection mode to a diagnostic object through the optical cable. Images of the diagnostic object are transmitted from the distal end of the endoscope assembly to the projection objective lens positioned on the proximal end thereof through the optical cable. A foldable dichroic optical splitter is positioned behind the projection objective lens as an optical path split means. As the mode changes between a normal endoscope mode and a fluorescent inspection mode, the position of the dichroic optical splitter is mechanically adjusted and the optical source positioned on the optical source module can be modified. The mode can be arbitrarily switched with a remote switch (e.g., a pedal).
In the fluorescent inspection mode, light inputted via the optical cable is split by the dichroic optical splitter into two paths leading to two TV cameras, respectively. The TV camera positioned in the first path has a color optical detection chip and is used to perceive images created by reflected excitation light. The TV camera positioned in the second path has a high-sensitivity monochrome (black and white) optical detection chip and is used to sense fluorescent images. An optical shield filter is positioned in front of the high-sensitivity monochrome optical detection chip in the second path to transmit light having fluorescent wavelength only. Signals from both TV cameras are transmitted to a computer. The computer's processor is programmed to control the operation of the TV cameras and process and analyze the images obtained from the TV cameras. Each frame from both TVs is displayed on a monitor.
Before endoscopic inspection is performed with the above endoscope system, the system is calibrated with a comparative fluorescent sample. For calibration, the endoscope assembly is positioned adjacent to the surface of the comparative fluorescent sample and light is irradiated. The resulting image (as shown in FIG. 7) of reflected light and fluorescent light are stored in the computer. The stored data is used to compensate for the irregularity of illumination to the diagnostic object and that of fluorescent images caused by the spatial difference of the degree of light collection in the field of view of the endoscope. The data is also used to determine when to replace the lamp and adjust the sensitivity of the equipment considering the aging of the lamp.
In order to perform a diagnosis based on quantitative analysis of fluorescent intensity, it is necessary to reduce the light measurement error caused by the change in distance from the distal end of the endoscope to the surface of the diagnostic object. To this end, a tool 36 is pushed out through a tool passage formed in the endoscope assembly 30 as shown in FIG. 3 and measurement is performed while maintaining a reference distance between the tool and the diagnostic object. Quantitative analysis of fluorescent intensity is preformed by analyzing the histogram of signal intensity distribution on the video frame.
The above-mentioned fluorescent endoscope system has problems as follows: in order to recognize from what part of the diagnostic object the fluorescent images are generated, both reflected excitation light and fluorescent light must be viewed on the same screen. If the reflected excitation light is partially transmitted to the high-sensitivity optical detection chip for sensing fluorescent light to this end, however, the accuracy of quantitative analysis deteriorates. The reflected excitation light and the fluorescent light are preferably detected via different paths. However, images of the reflected excitation light and those of the fluorescent light, which have been obtained separately, must be superimposed and displayed on the same screen. Although the above fluorescent endoscope system according to the prior art uses two cameras to separately detect reflected excitation light and fluorescent light for improved accuracy of quantitative analysis, the cameras are operated asynchronously and, when image signals of reflected excitation light and fluorescent light obtained from both asynchronously operated cameras are successively inputted to a computer via a PCI bus, a number of frames are lost due to difference in frame timing. In addition, the system speed decreases when images from reflected excitation light and fluorescent light are displayed on a monitor. Therefore, the problem of timing difference of the image data obtained from both cameras must be resolved. In order to display superimposed images, the size of images detected from both cameras must coincide. When signals obtained from different cameras are separately processed according to the prior art, however, such coincidence is difficult to occur.
In the above fluorescent endoscope system, the distance between the distal end of the endoscope and the diagnostic object is mechanically maintained with a tool for quantitative analysis of fluorescent intensity in a fluorescent inspection mode. Such mechanical maintenance of distance is vulnerable to errors resulting from diagnostic environments (e.g., fine vibration) and has limited diagnostic accuracy.
In order to independently drive two cameras, furthermore, separate driving circuit and data process module must be installed. This makes the system very complicated.